1. Field of the Invention
The present invention relates to a polymeric centralizer for centering pipe strings in well bores or within in other pipe strings which can be easily fitted onto a production string or casing during down hole insertion.
More particularly, the present invention relates to a polymeric centralizer for centralizing pipe strings in well bores and within in other pipe strings including a plurality of blades or fins extending substantially longitudinally along an outer surface of the centralizer, a slit through a blade opposite a groove for opening the centralizer so it can be fitted onto a production string or casing, a fastener means for securing or tightening the centralizer to the string or casing and cutaways for allowing wirelines or cables to pass between the centralizer and the production string to protect the cable, where the centralizer is wear and abrasion resistant, safe for use in hazardous environments and does not contribute to metal contamination of the well.
2. Description of the Related Art
In the completion of oil and gas wells it is standard practice to set or cement at least one string of casing within the well bore. Casing strings are cemented in the well bore to prevent fluids from migrating from the production zone through the annulus between the casing string and the well bore to the surface or other zones where for example fresh water may be contaminated. In addition, there are regulations which require that some zones be cemented off.
In cementing a casing string, a cement slurry is pumped down the interior of the casing string, out the lower end, into the annulus between the string and the well bore. However, to effect an efficient cementing job, the complete annulus needs to be cemented without pockets in the cement and without areas in which the string is contacting the wall of the well bore. To facilitate obtaining an effective cementing job the casing is commonly centered in the well bore with centralizers which are disposed about the casing string. In addition, the centralizers aide in running the pipe into the hole without hanging up.
Centralizers may also be used on casing or pipe strings, such as tubing, which are hung within another string of casing or pipe. These inner strings may be cemented within the outer pipe string or they may not be.
Centralizers for casing, tubing or pipe commonly are constructed of a low carbon steel having a tubular body or sleeve adapted to fit around a pipe joint. These prior art centralizers usually include outwardly bowed springs having opposing ends connected to opposite ends of the sleeve. Although the resiliency of the bow strings enables them to move through tight spots in the well bore, they may not support the weight of the casing string, especially in a highly deviated well bore.
In another type prior art centralizer, the bow strings are replaced by solid strips of metal which are tapered at each end to provide outer spaced bearing surfaces for engaging the well bore or the outer casing. Although less prone to collapse than bow springs under the weight of the casing string, these metal strips are often not strong enough to prevent bending upon contacting an obstruction or turn in the well bore. As a result, the centralizer and the casing may become wedged in the well, and, in any case become unsuitable for providing a suitable cementing job.
Another type of prior art centralizer is a non-metallic sleeve centralizer disclosed in U.S. Pat. No.; 5,908,072.
These prior art metal centralizers have further drawbacks, especially, when run and set within another string of pipe. One of the drawbacks of metal centralizer is contact with the outer pipe when the string vibrates. Metal to metal contact may cause a spark, which can be very hazardous in the hydrocarbon filled well. Also, metal centralizers can create a corrosion problem with the casing strings which it contacts through electrolysis. Metal centralizers also are susceptible to damage when running acid and circulating the acid back out of the hole. Additionally, there is a concern with scrapping the inner diameter of stainless steel tubing when running stainless/duplex stainless steel tubing having metal centralizers. The non-metallic sleeve centralizers overcome some of these disadvantages, but sleeve type centralizer are difficult to attach to pre-connected strings.
It would be a benefit, therefore, to have a polymeric centralizer adapted to fit about a string of pipe for centering the pipe in a well bore or within an outer string of pipe such as a production riser which can be easily attached to the string prior to or after make-up. It would be further benefit to have a polymer centralizer that can be used with downhole operations that require control cabling or umbilicals or wirelines where the cabling can be inserted through slots or cutaways in the centralizer.